Plants are more brittle in cold temperatures. Messing around with them may cause branches to snap and split unintentionally. It's minor, but it could impact the look of a plant or create a haven for insects and diseases later. Don't prune when the temperature falls below 25°F.
Any gardening expert will tell you, (contrary to what you may believe) that pruning encourages new growth just when the plant is trying to go dormant and new growth doesn't have enough time to harden before the first frost and freezing temperatures hit. Pruning at this time of year will severely weaken the plants.
An improper cut like a flush cut (cutting too close to the trunk) or a stub cut (cutting too far from the trunk) can cause irreversible damage to a tree. A flush cut removes the branch collar and leaves a large wound in the side of the tree that won't heal properly.
Follow The 1/3 Rule
It involves trimming around 1/3 of the branch, as cutting more than that may increase the chances of damage or stunt its growth. However, pruning too little will not give you the desired result.
What is improper pruning? Cutting too close to the nodes or too far from the trunk is referred to as improper pruning. It can cause irreversible damage to your plants. What types of pruning are often done? Thinning cuts, reduction cuts, and heading cuts are often done to prune a plant.
If you want to prune in fall, wait until trees drop their leaves and are dormant—usually October or November. After leaf drop, you can see the tree's structure and identify disease and insect problems more easily.
Generally, the best time to prune or trim trees and shrubs is during the winter months. From November through March, most trees are dormant which makes it the ideal time for the following reasons: Trees are less susceptible to insects or disease.
The best time to prune is after flowering. If the plant needs to be renovated, or severely reduced, this can be done late winter and early spring just before growth begins.
As a general rule, prune spring-blooming trees immediately after they flower. Prune trees that bloom in the summer or fall in late winter or early spring before the end of their dormancy. Routine pruning of dead or dying branches can be done at any time.
When to Cut Back Hostas. As a general rule, hostas should be cut back in the late fall. Start with leaves that have wilted or turned brown. Healthy leaves can stay a bit longer to help the roots store needed energy.
Late summer or early fall pruning causes vigorous re-growth of tissue, which in some cases may not harden off by the time winter arrives, leading to possible cold damage to the new growth.
Don't Prune in Late Summer and Fall
Pruning shrubs in August or early September may encourage a late flush of growth.
"As soon as trees and shrubs go into dormancy, pruning can begin," he said. "And you can prune up to the time when buds begin to plump up." From mid-November to mid-March, you can shape and thin your deciduous plants in preparation for the spring season ahead.
The best season to prune trees is while they are dormant, or generally between November and March. This means waiting for them to lose their foliage and cease growth, but before forming buds. For fruit trees such as the apple tree, prune in late winter.
Winter is usually the best time.
Dormant pruning is usually done in late winter, six to 10 weeks before the average last frost in your area. You can prune shrubs at any time of year if it's necessary—for example, to remove broken branches or dead or diseased wood, or to remove growth that is obstructing a walkway.
Never shear a shrub in fall (or ever, actually, but that's another article) and leave major pruning or renovation for late winter/early spring, or immediately after bloom for spring-flowering shrubs.
Choose the Right Time
Likewise, prune in the early morning or late afternoon to avoid the newly cut ends of branches becoming scorched by the hot sun. Wait 48 hours after rain to prune, to allow plants to dry out and avoid fungal diseases. When pruning, make cuts just above leaf nodes, or buds.
The 1/3 rule involves cutting about 1/3 of wood during any pruning activity. This moderate pruning practice is a balanced approach to thinning out shrubs to stimulate new growth. The plant loses a good amount of stems, usually on the top section, allowing more light and air to enter the inside of the plant.
Some have learned that pruning wounds should be sealed with a pruning compound to “protect” the plant from insects and pathogens. However, scien- tific research tells us that pruning compounds and sealants actually do more harm than good when applied to plants (with one exception which I will mention later).
ALWAYS prune back to or just above a growing point (branch or bud) or to the soil line. NEVER leave a stem or branch stub. NEVER top a tree to “rejuvenate” growth.